Proposals have been made of a linear motor comprising a shaft member made of a permanent magnet having alternately arranged N and S poles, and a coil unit having a plurality of coils arranged in an axial direction so as to surround the shaft member (see, for example, the Unexamined Japanese Patent Application Publication (Tokkai-Hei) No. 10-313566).
The linear motor disclosed in the Unexamined Japanese Patent Application Publication (Tokkai-Hei) No. 10-313566 is used in OA equipment or the like, for example, in place of a combination of a rotary motor and a ball screw. Also for machine tools such as press machines which make direct-acting motion, the use of the linear motor simplifies the configuration and enhances controllability. However, when the linear motor is used for the press machine, a high thrust needs to be obtained. The linear motor generally uses a permanent magnet with a strong magnetic force. However, it is difficult to manufacture linear motors each generating a high thrust, because of manufacturing limits on the size of the magnet and restrictions on a supplied voltage and the like.
A linear motor having a plurality of juxtaposed cylindrical linear motors has been proposed. However, in this linear motor, each of the cylindrical linear motors has a guide mechanism that moves a shaft member forward and backward with respect to a coil unit. Thus, disadvantageously, the linear motor has a large, complicated structure, increasing costs.